Linear scaling between microbial predator and prey densities in the global ocean

Area of Science:

• Marine ecology
• Microbial ecology
• Ecological stoichiometry

Background:

• Previous studies proposed sublinear power laws for microbial predator-prey biomass and abundance.
• These relationships are crucial for understanding marine food web dynamics and microbial loop functioning.

Purpose of the Study:

• To re-evaluate the biomass scaling relationships between marine microzooplankton predators and phytoplankton prey (Z/P).
• To re-evaluate the biomass scaling relationships between marine viral predators and bacterial prey (V/B).
• To test the hypothesis of sublinear power laws against alternative models.

Main Methods:

• Analysis of previously published biomass and abundance data.
• Fitting Power-law Biomass Scaling Relationships (PBSRs) using Type II regression models.
• Type II regression accounts for errors in both independent and dependent variables, unlike conventional Type I regression.

Main Results:

• Data support linear relationships between predator and prey biomass, contradicting previous sublinear findings.
• The scaling exponent has an expected value of 1, with variations described by a Gaussian distribution.
• The ratios of microzooplankton to phytoplankton (Z/P) and viral to bacterial (V/B) biomass are, on average, invariant.

Conclusions:

• The findings challenge the hypothesis that predator/prey ratios systematically decrease with increasing prey biomass.
• Microbial predator-prey biomass scaling is characterized by linear relationships and invariant ratios.
• This suggests a fundamental difference in how microbial communities scale compared to previous assumptions.